The typical residential furnace uses a plurality of natural or gravity draft burners in conjunction with a so-called clam shell type heat exchanger. Such heat exchangers typically are of the sectional design with individual sections connected near the bottom and connected to a common flue-gas breeching at the top with an individual burner at the bottom of each section. Such heat exchangers do not lend themselves to installation in a so-called compact furnace which typically requires a tubular heat exchanger coupled with a forced draft or power burner. However, with a power burner to be used in a domestic compact furnace there are relatively stringent technical requirements, as well as cost and size requirements from a manufacturing and marketing standpoint. As to the technical requirements, the American Gas Association sets performance levels on the flue temperature, materials temperatures, and carbon monoxide concentration in the flue which results in a minimum efficiency for AGA certification. To market a compact furnace competitively, the cost of manufacture of the furnace must be kept relatively low. If the furnace is to be considered compact, it must be of limited size. In my view, if all of these requirements are to be met, the attainment of good fuel-air mixing is relatively difficult since a low air pressure requirement restricts the mixing levels, exotic mixing devices such as vanes, etc. increase cost, and the size restrictions for a compact burner require that good mixing take place in a relatively short distance. While gaseous fuel can be injected into the inlet of a combustion air blower to get good fuel air mixing, the code restrictions require with such an arrangement that the motor be explosion proof, which of course adds significant cost.
As to the prior patent art, examples of patents showing power gas burners in which the air is fed axially into a mixing chamber or combustion chamber include U.S. Pat. Nos. 3,801,212, 3,489,134, 3,032,096. Examples of burners using a refractory material at a combustion location include U.S. Pat. Nos. 3,635,644 and 1,215,229. An example of a U.S. patent showing the introduction of primary air and secondary air of combustion in a tangential arrangement is found in U.S. Pat. No. 2,018,582. It is my view that none of these arrangements would be satisfactory to meet the objects of the arrangement according to my invention.